Field of the Invention
The present invention relates to golf balls. Specifically, the present invention relates to golf balls including a core, a mid layer, and a cover.
Description of the Related Art
The greatest interest to golf players concerning golf balls is flight performance. Golf players particularly place importance on flight distances upon shots with drivers. A flight distance upon a shot with a driver correlates with the resilience performance of a golf ball. When a golf ball in which a core having high resilience is used is hit, the golf ball flies at a high speed, and a large flight distance is achieved.
In order to obtain a large flight distance upon a shot with a driver, a core having an outer-hard/inner-soft structure may be used. When a golf ball including a core having an outer-hard/inner-soft structure is hit with a driver, the spin rate is suppressed, and the launch angle becomes large. The low spin rate and the large launch angle achieve a large flight distance.
There have been various proposals for improvement of flight performance. For example, JP2011-217857 (US2011/0250991 A1) discloses a golf ball including a core in which: the difference between a JIS-C hardness H(5.0) at a point to which the distance from the central point of the core is 5 mm and a JIS-C hardness Ho at the central point is not less than 6.0; the difference between a JIS-C hardness H(12.5) at a point to which the distance from the central point is 12.5 mm and the hardness H(5.0) is not greater than 4.0; the difference between a JIS-C hardness HS at the surface of the core and the hardness H(12.5) is not less than 10.0; the difference between the hardness HS and the hardness Ho is not less than 22.0; and there is no zone in which the hardness decreases from the central point of the core toward the surface of the core.
JP2013-230365 (US2013/0296072 A1) discloses a golf ball in which a JIS-C hardness (H−14) at a position that is inward from the surface of a core toward the central point of the core by 14 mm, a JIS-C hardness (H−8) at a position that is inward from the surface of the core toward the central point of the core by 8 mm, a JIS-C hardness (H−6) at a position that is inward from the surface of the core toward the central point of the core by 6 mm, and a JIS-C hardness (H−4) at a position that is inward from the surface of the core toward the central point of the core by 4 mm satisfy relational expressions of (1) H−14<70, (2) H−8<72, (3) H−6<75, and (4) H−4−H−8>8.
JP2015-77405 (US2014/0100059 A1) discloses a golf ball in which relational expressions of (1) D−C≥7, (2) C−B≤7, (3) (D−C)−(C−B)≤7, and (4) E−A≥16 are satisfied when the radius of a core is denoted by R (mm), a JIS-C hardness at the central point of the core is denoted by A, a JIS-C hardness at a position away from the central point of the core by R/3 mm is denoted by B, a JIS-C hardness at a position away from the central point of the core by R/1.8 mm is denoted by C, a JIS-C hardness at a position away from the central point of the core by R/1.3 mm is denoted by D, and a JIS-C hardness at the surface of the core is denoted by E.
Golf players also place importance on controllability of golf balls. Particularly, the level of interest to golf players concerning controllability (approach performance) upon approach shots is high. The controllability correlates to the spin rate of a golf ball. When the rate of backspin is high, the run is short. By using a golf ball having a high backspin rate, a golf player can cause the golf ball to stop at a target point. When the rate of sidespin is high, the golf ball tends to curve. By using a golf ball having a high sidespin rate, a golf player can intentionally cause the golf ball to curve.
With a golf ball in which a spin rate upon hitting with a driver is reduced in order to obtain a large flight distance, the spin rate upon an approach shot also becomes low, and the controllability may decrease. Further improvement of a flight distance upon a shot with a driver while satisfying a demand of golf players on controllability is desired.
An object of the present invention is to provide a golf ball having excellent flight performance and approach performance.